( io 6 ) 
He refers to bis Cometograpby thefe Difquifitions i whe- 
ther ail Comets (in their innate Motion) move equal Space t 
in equal Times .<? which is the (wiftelf , and which the (loweft 
Motion they are capable of? what the caufeof this accele- 
ration and retardation of their true Motion ? 
He puts it out of doubt, that they are in the sky it felfj 
producing Reafons for it that are very confiderable, and al* 
lodging among others, 7 hat the Parallaxes doe clearly e- 
vince it, vvhich he finds far lefs in Comets, then in the Mock , 
yea then fometimes in the Sun it fe!f. Where he aifo repre~ 
lents, That he harh deduced the Horizontal Parallax of this 
very Comet from one onely Obfervation, made Febr : 4. /?.». 
by which he found, That then it was diftant from the Earth 
5000 Semidiameters of the fame, or 4500000 German miles, 
f rom this its diftant from the earth,he deduces, That on that 
Day when it wa s fo remote from the Earth,its true Diameter 
was 2 560 German miles, which is three times bigger then the 
Diameter of the Earth, and almdft fix times bigger then 
that of the Moon, whofe Diameter,according to his 7 heory^ 
is 442 German miles. 
Befinds the Matter of Comets to be in the JE'ther it felf, 
making the JEthcr and the Air to differ onely in purity, and 
■tfteeming, That the Planets do emit their Exhalations, and 
have their Aimofpheres like unto our Earth. Where he af- 
firms, ThattheSun alone may calf out fo much Matter at 
any time in one Year, as that thence (hall be produced not 
one or two Comets, equalling the Moon in Diameter, but 
very many 5 which if fo, what contribution may not be 
■expe&ed from the other Planets? 
Of this Cometical Matter^ he thinks. That firfi it is by 
Iktfe and little gathered together, then coagulated and con * 
denfied, and thereby reduced to a lefs Diameter $ but then-, 
after .a while, it refolves again, and grows dilute and na ie, 
and at faff is diffipated. And accordingly he affirms. That 
he hath observed 1 he Head of this Comet at firft. more con - 
jfufed, thin and pale, afterwards clearer and clearer. 
He 
